In general, an objective optical system for acquiring images of an observation object and an illumination optical system for irradiating the observation object are arranged at the tip portion of an insertion section of an endoscope. Furthermore, an imaging device that acquires images of the observation object imaged by the objective optical system is installed in the insertion section.
Furthermore, a first lens of the objective optical system and a first lens of the illumination optical system are disposed on the tip surface of the insertion section of the endoscope, and these first lenses may break or chip due to an impact caused by collision etc. In particular, with a thin endoscope, even though the first lenses are disposed near the center of the tip surface, they are subject to direct impact and breakage because the distances from the side surface are short.
Furthermore, in conventional techniques, after the objective optical system and the illumination optical system are individually assembled, the task of assembling them in the tip part is performed.
A technique in which the tip part is made of a plastic material, and the first lenses, which are parts of the objective optical system and the illumination optical system, are formed integrally with the tip part has been disclosed (for example, see PTLs (Patent Literatures) 1 to 4).